ORBIT OF MERCURYASTR 110G Section M09

September 30th, 2010

http://www.nso.edu/press/archive/merc_transit/mercury_transit_composite03.jpg

PLANETARY ORBITS

All planets orbit the Sun on an ellipse Semi-major axis: a, half of longer axis length Period: P, the time it takes a planet to go

around the Sun once Eccentricity: e, measure of how “stretched”

the orbit is from a circle e = 0: orbit is a circle 0 < e < 1: orbit is an ellipse with 1 being very

stretched and 0 being circular e = (ra – rp)/(ra + rp)

ra is the farthest a planet is from the Sun rp is the closest a planet is from the Sun

MERCURY’S ORBITAL PARAMETERS

WRITE THESE DOWN! You need them for your summary

Period: 87.969 days Semi-major axis: 0.387 AU Eccentricity: 0.2056

GREATEST ELONGATION

Greatest Eastern Elongation

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http://www.astro.lsa.umich.edu/undergrad/Labs/planetMotions/elongation.gif

WHAT YOU HAVE TO DO Work in pairs (or three people if you have an

odd number in your group) to create Mercury’s orbit Do calculations, then find all Earth positions, then

all Mercury positions. LABEL EVERYTHING! Each person should find some of the Earth and

Mercury positions – 2 people: 6-7 positions each, 3 people: 4-5 positions each

Check with me to be sure your first couple points are correct

Once done with that, compare orbits to rest of group and pick best orbit. Ask me if you are unsure

Work on the rest of the lab in groups using the best orbit and attach it to group lab

EA

RTH

PO

SIT

ION

S

• Large circle is orbit of Earth

• Arrows on orbit represent direction Earth is moving around Sun

• Sun is the center dot

EA

RTH

PO

SIT

ION

S

1. Draw dashed line between Earth (X) and Sun (center dot)

2. Line up bottom edge of protractor on line with center on Sun

3. Measure out calculated angle (last column of Table 7.1) from previous Earth position to get new Earth position

42°

EA

RTH

PO

SIT

ION

S

1. Draw a dotted line between the Sun and your new Earth position

2. Label this position so you know what line this is later

EA

RTH

PO

SIT

ION

S

1. Again, line up the bottom edge of protractor on Earth-Sun line with Sun at center and Earth at 0°

2. Measure out calculated angle and mark it

3. Draw dashed line between Sun and new position

4. Label position

72°

EA

RTH

PO

SIT

ION

S

• This is what all 13 positions should look like

• All should be labeled with dotted lines between Earth and Sun

MER

CU

RY

PO

SIT

ION

S

1. Line bottom edge of protractor with Earth-Sun line

2. Earth at center of bottom of protractor

3. Measure out given angle (column 3 in Table 7.1) – position #1 has east angle

East angle: left of the Sun

West angle: right of the Sun

27.2°

MER

CU

RY

PO

SIT

ION

S

1. Draw solid line between Earth and mark from measured angle

2. Be sure the line goes past Earth – necessary for the next step

3. Mercury is located somewhere on this line

MER

CU

RY

PO

SIT

ION

S

1. Place the protractor so that the solid line goes between the center of the bottom and the 90° tick

2. Keeping that alignment, line up the bottom of the protractor with the Sun

3. Where the protractor bottom intersects the solid line, place a dot

GREATEST ELONGATION

Greatest Eastern Elongation

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http://www.astro.lsa.umich.edu/undergrad/Labs/planetMotions/elongation.gif

MER

CU

RY

PO

SIT

ION

S

1. Place the protractor so that the solid line goes between the center of the bottom and the 90° tick

2. Keeping that alignment, line up the bottom of the protractor with the Sun

3. Where the protractor bottom intersects the solid line, place a dot

MER

CU

RY

PO

SIT

ION

S

1. Position #2 has a west angle so angle must be measured to the right of the Sun

2. Line up protractor and measure angle to the left of Sun

3. Draw solid line between Earth position 2 and new angle mark

18.1°

MER

CU

RY

PO

SIT

ION

S

1. Line up protractor at 90° on Mercury line

2. Line bottom of protractor on Sun

3. Mark where bottom of protractor crosses Mercury line

4. Label Mercury locations based on Earth position #’s

MER

CU

RY

PO

SIT

ION

S

• This is what all 13 Mercury positions should look like

• Each position should be labeled same number as corresponding Earth position (needed for later question in lab!)